Manchester United have no competition up front - Jose Mourinho

Anthony Martial fired in a shot off the crossbar to see Manchester United past Burnley in a tight affair at Turf Moor.

With Jose Mourinho set for a contract extension, Paul Mariner and Alexis Nunes debate whether his tenure at Man United will be the defining moment of his career.

Manchester United manager Jose Mourinho insists the club's pursuit of Alexis Sanchez has been driven by a need for more competition for places in his squad.

Mourinho watched Anthony Martial score the only goal of the game against Burnley to hand United their fourth consecutive win.

Martial started on the left in a front four which also included Jesse Lingard, Juan Mata and Romelu Lukaku.

But with Zlatan Ibrahimovic still sidelined with a knee injury, Marcus Rashford was the only attacking player on the bench -- a problem Mourinho says he hopes to solves by signing Sanchez.

"In this moment, there is no competition for places," he said. "At this moment, we have four attacking players for three positions, one on the bench, Zlatan for whole season was not available.

"We look to attacking areas, and we need that extra internal competitiveness."

United were made to work hard by Burnley, who have now gone eight games without a win. Martial came up with the only outstanding moment of the game after picking up Lukaku's pass to fire in off the underside of the crossbar after 54 minutes.

It was one of only two shots on target United managed all afternoon but after keeping a fifth clean sheet in a row, it was enough to keep up some pressure on leaders Manchester City.

"It's a different kind of performance to try to have but is a performance needed to get a result needed against a brave team like Burnley," Mourinho said.

"We know the way they play, they are better than anyone playing that way, we had to adapt to be successful and we adapted well by the defensive point of view.

"We should have scored a second goal to kill it off and put ourselves in a position to fight until the last second, and the best image of it was with [goalkeeper Nick] Pope in the box for the last couple of crosses and that's the image of how competitive the game was."

Rob is ESPN FC's Manchester United correspondent. Follow him on Twitter @RobDawsonESPN.